Known snow groomers normally comprise a hydraulic control device connected to a pump; lines connecting the pump to an attachment hydraulic assembly; and an internal combustion engine connected to and for driving the pump.
In actual use, the pump is controlled by the hydraulic control device as follows:                When the hydraulic assembly actuator is idle, the valve is closed and the pump is controlled by the hydraulic control device so that the pressure in the lines equals a standby pressure.        When the hydraulic assembly actuator is active, the valve is open and the pressure in the lines falls below the standby pressure.        When pressure falls below standby pressure, the hydraulic control device acts on the pump to deliver the maximum possible flow rate, which varies depending on the operating conditions, in particular the speed, of the internal combustion engine.        
In other words, the instant the actuator is operated, the pump delivers the maximum flow rate, even if the actuator does not need it; in which case, the valve delivers the necessary flow rate to the actuator, and the difference between the maximum flow rate from the pump and the necessary flow rate is drained into a holding tank.
One drawback of certain known snow groomers lies in the pump delivering the maximum flow rate, even if the actual flow rate demanded by the actuator is lower.
Another drawback of certain known snow groomers lies in unnecessary operation of the pump, which consists in the valves draining surplus flow into the holding tank, and which subtracts energy from other groomer user devices.
Both drawbacks are compounded by the pump being configured to feed a plurality of hydraulic assemblies, and by each hydraulic assembly possibly comprising more than one valve.